“There were just times, a couple of times, where we would try to get a why,” said Anchorage Police officer Jeff Bell, who helped interrogate Keyes for hours.

“He would have this term, he would say, 'A lot of people ask why, and I would be, like, why not?'” Bell said.

Keyes confessed to killing eight people across the United States, but alluded to additional killings, FBI Special Agent Jolene Goeden and Bell told The Associated Press.

“Based on some of the things he told us, and some of the conversations we had with him, we believe the number is less than 12,” Goeden said. “We don't know for sure. He's the only one who could have ultimately answered that.”

They may never know the true number.

Keyes slit his wrist and strangled himself with bedding Sunday at the Anchorage Correctional Facility. He was facing a March trial on federal murder charges in the kidnapping and death of 18-year-old Samantha Koenig, who was abducted from an Anchorage coffee stand Feb. 1.

He also wasn't going to stop. Authorities said he had weapons caches or body disposal kits stashed across the country. One kit found north of Anchorage included a shovel, plastic bags and bottles of Drano, which he told authorities would speed the decomposition of bodies.

Keyes confessed to killing Koenig, along with Bill and Lorraine Currier in Vermont, and five other people — although details for those victims were scarce.In the case of the Curriers, authorities say Keyes flew from Alaska to Chicago on June 2, 2011, rented a car and drove almost 1,000 miles to Essex, Vt. There, he carried out a “blitz” style attack on the Curriers' home, bound the couple and took them to an abandoned house, where he killed them.